<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let cj = +prompt('请输入成绩');
        if (cj >= 90) {
            alert('成绩优秀')
        }
        else if (cj >= 70 && cj < 90) {
            alert('成绩良好')
        }
        else if (cj >= 60 && cj < 70) {
            alert('成绩及格')
        }
        else if (cj < 60) {
            alert('成绩不及格')
        }
    </script>
    </bosdy>

</html>